The invention relates to an improved extended nip press and more particularly to a pressing mechanism for extracting water from a traveling web which requires considerably less space and is capable of extracting more water from the web than has been heretofore possible with conventional press couples.
The present invention provides a pressing arrangement having a plurality of nips wherein the residence time of the web in the nips is increased over that of a roll couple and wherein a mechanically more compact structure is used. Attempts have been made to provide presses which provide for a greater pressing time and reduce the space required by the press, but a number of these have encountered disadvantages, and the present structure provides advantages over structures heretofore available.
As will be appreciated from the teachings of the disclosure, the features of the invention may be employed in the dewatering of other forms of webs than a paper web in a paper making machine. However, for convenience, a preferred embodiment of the invention will be described in the environment of a paper making machine which conventionally forms a web by depositing a slurry of pulp fibers on a traveling fourdrinier wire, transfers the web to a press section where the web passes through a number of press nips formed between roll couples, and the web then passes over a series of heated dryer drums and usually through a calendar and then is wound on the roll. The present structure forms the entire press section and takes the place of other forms of press sections heretofore available. Modifications can be made in the overall machine, as to the forming section, or the dryer section which can be accommodated by the instant invention. The structure of the instant disclosure also may be employed in pressing webs of various synthetic fibers.
The present invention relates to improvements for the press sections of a paper making machine. Because of various inherent limitations in the operation of roll couples forming press nips for the press section in a conventional paper making machine, only a given amount of water can be removed in each nip and, therefore, in a conventional paper making machine, a series of nips are usually employed. It has been found impractical to attempt to remove a significant amount of additional water by increasing the number of press nips, although the further removal of water by pressing can greatly reduce the expense and size of the dryer section. It is estimated that if the water removed in the press section can be increased to decrease the moisture from 60 percent to 50 percent, the length of the dryer section can be reduced by 1/3. This is significant in a typical 3000 feet per minute newsprint machine which employs on the order of 100 dryer drums. This significance can be appreciated in considering that the dryer drums are each expensive to construct and to operate and require the provision of steam fittings and a supply of steam for each drum. The relative importance of the removal of water in the press section is further highlighted by the fact that one of the most important economic considerations in justifying a satisfactory return on investment in the operation of a paper making machine is to obtain the highest speed possible consistent with good paper formation and better pressing will shorten the necessary time in the dryer section and permit higher speeds.
It is accordingly an object of the present invention to provide an improvement in the press section of a paper machine which makes it possible to remove an increased amount of water in this press section and makes it possible to provide a press section having a relatively compact or shortened pressing area of a unique elongated or extended nature which does not have the performance limitations of conventional roll couple presses and which requires far less space in terms of requirements as to the overall length of the press section. By increasing the amount of water removed from the web in the press section, increased speeds are possible with existing equipment, i.e., a given length of dryer section can operate at higher speeds since it is required to remove less water. Also, new equipment can be constructed requiring less machine length and expense.
It is an object of the present invention to provide a press using a traveling belt wherein an improved structure is employed for applying the nip loading pressure to the belt.
A further object of the invention is to provide an improved pressing mechanism for a press which counteracts the disadvantageous effects of friction and provides a press which has a uniquely long operating life.
Another object of the invention is to provide a press mechanism wherein pressures at stages along the nip are more easily controlled than in structures heretofore available.
Another object of the invention is to provide a press which avoids the disadvantages of excessive leakage and the difficulty of providing large sliding seals as contrasted with prior art liquid pressure presses.
Other objects, advantages and features will become more apparent with the disclosure of the principles of the invention and as will be seen, equivalent structures and methods may be employed within the principles and scope of the invention as taught in connection with the description and disclosure of the specification, claims and drawings, in which: